N-PROCESS-LEVEL REGULATION OF NITROGEN TRACE GAS FLUX IN HAWAIIAN MONTANE RAIN-FOREST

Nutrient amendments and inhibition experiments were used to evaluate f actors controlling the production of N trace gases in soils. Sampling was conducted at five sites which form a 200-4.5 x 10(6) y chronoseque nce in Hawaiian montane rainforest. The pattern of nitric oxide (NO) a nd nitrous oxide (N2O) flux from soils in the laboratory was similar t o that observed in the field, with emissions of NO + N2O increasing wi th soil age. Autoclaving of soils indicated that there was little or n o abiological production of N2O. The response of N2O and NO flux to si eving and acetylene addition is consistent with N trace gas production being primarily denitrification-based in all but the oldest site, whe re nitrification-based production is significant. All the soils had in creased emissions of N2O in response to additions of N. Soils from the 185,000-y-old Kohala site, however, had the lowest proportional N2O r esponse, did not have elevated NO emissions in response to addition of N, and had a small, but significant NO response to addition of carbon . This intermediate-age site represents a transition stage in soil dev elopment in which N trace gas production is the least limited by N-ava ilability. Copyright (C) 1996 Elsevier Science Ltd